A lifelong swimmer, Tracey McCormick routinely trains for competitions. But there was no preparing for the life-saving plunge she took last month.

Tracey, a logistics manager at Gap Inc. headquarters in San Francisco, was returning home from a Father’s Day barbecue, driving along an estuary in Oakland, Calif. when she caught sight of a sedan half-submerged and sinking fast about 25 feet from shore. No soul was in sight on land or in the water.

“Then I saw hands on the back of the window,” she said. “I didn’t think for a second.”

Tracey pulled over, jumped from her car and dove into the bay. The chilly water normally would have taken her breath away. On that afternoon, she didn’t notice.

The car’s front doors were already underwater. The back doors wouldn’t budge. The windows were rolled up tight. And trapped inside and pounding desperately on the rear glass were a boy and girl. If their parents were inside, Tracey could not see them and she feared the worst.

She treaded water helplessly, pulling at door handles, banging on the glass and watching the children shift and struggle for air.

“I thought it was going to go down right here, right now and I would watch them drown and there was nothing I could do,” she said. “There was maybe 12 inches of air left at the back window.”

Two more passers-by had joined her by then – one man who swam out to the vehicle and the other who fetched a paramedic tool to break the glass from a passing ambulance.

Tracey fumbled, at first, with the 5-inch device, trying to use the sharp end on the window, before passing it to her co-rescuer, who shattered the pane. They pulled out the children and the mother and father -- still alive -- and got them safely to shore.

“It doesn’t surprise me at all that Tracey jumped in to help,” said her supervisor Ignacio Vaca, Gap Inc. logistics director. “No matter what the problem is, she always thinks, ‘Yes, we can do this.’ That’s who she is.”